If I compile the Subscriber in which there is the "import nest" command I obtain: salvo@salvo-Aspire-GX-781:~$ rosrun pacchetto_ros sub_vrep.py Traceback (most recent call last): File "/home/salvo/Desktop/ros_ws/src/pacchetto_ros/scripts/sub_vrep.py", line 5, in <module> import vrep ImportError: No module named vrep